We never proposed there was no lower bound; the goal was more to discover where it was. And we now have, I think. Though in fact the main thing we discovered was how fuzzy it is.

There really are people who can start a startup when they're 19. Sam Altman, the founder of Loopt, was 19. But for most people the lower bound is about 22. One reason is that most people need to experience what a job is like to be sufficiently motivated to avoid it. Another is that few people are forceful enough at 19.